Slow Chain Dynamics in Isotactic-poly(4-methyl-1-pentene) Crystallites near the Glass Transition Temperature Characterized by Solid-State 13 C MAS Exchange NMR Toshikazu Miyoshi,* ,† Ovidiu Pascui, ‡ and D. Reichert* ,‡ Research Center of Macromolecular Technology, National Institute of Advanced Industrial Science and Technology (AIST), Tokyo-Water-Front, 2-41-6 Aomi, Kohto-ku, Tokyo, Japan, and Fachbereich Physik, Martin-Luther-Universita ¨ t Halle-Wittenberg, 06108 Halle, Germany Received March 16, 2004; Revised Manuscript Received June 15, 2004 ABSTRACT: The chain dynamics for isotactic-poly(4-methyl-1-pentene) (iP4M1P) crystallites near the glass transition temperature (T g ) 304 K) is characterized by solid-state 13 C MAS NMR methods at natural abundance. The 13 C line width under high-power proton decoupling and the 13 C spin-lattice relaxation time in the rotating frame (T1Fc) detect the segmental motions in the amorphous and crystalline regions with correlation times of about 0.2 × 10 -5 s at 360-382 K and about 448 K, respectively. Centerband- only detection of exchange (CODEX) with an additional T1Fc filter is applied to investigate the motional geometry and kinetic parameters for the main- and side-chain dynamics in iP4M1P crystallites in a sample. The CODEX evolution-time dependence of the resolved signals indicates a large-angle reorientational process: the simulation of the experimental data of the main-chain CH 2 signal reveals that iP4M1P crystallite performs the helical jump motions with jump angles of 72-145° in the disordered 72 helix. The CODEX mixing-time dependence permits the determination of kinetic parameters for the main- and side-chain motions over about 4 orders of magnitude. The determined correlation times for the main- chain carbons match these of the side-chain signals over the investigated temperature range, indicating that the side chain does not perform an independent slow dynamic process in the crystallites. The temperature dependence of the correlation time does not obey an Arrhenius behavior but must be analyzed in terms of WLF behavior with a reference temperature of T s ) 294 K. This exceptional behavior of a crystalline material is explained in terms of the amorphous and/or interfacial constraints around Tg. Furthermore, 2-D exchange NMR shows that helical jump motions accompany conformational transition. We also discuss our NMR results in relation to previously reported bulk mechanical relaxation and other data. Introduction The mechanical R relaxation in the crystalline region (R c ) for a semicrystalline polymer plays an important role in the bulk material properties such as crystalliza- tion, creep, drawability, and probably crystal-crystal transformation. The understanding of the R c relaxation is, therefore, one of the most important topics in the polymer science field. So far, there are many experi- mental results and theoretical considerations for the elucidation of the R c relaxation. 1-12 Among them, ad- vanced two-dimensional (2-D) solid-state exchange NMR methods have been successfully applied to investigate microscopic dynamic nature in the crystallites around the R c relaxation temperature region. 4-12 Solid-state 2-D exchange NMR observes the molecular dynamics driven reorientation of the 13 C chemical shift anisotropy (CSA) or the 2 H quadrupole tensor, which are tightly connected to the atoms and provide detailed information about the geometry of motions and kinetic parameters. For poly- (ethylene) (PE), 6 isotactic-poly(propylene) (iPP), 7,8 poly- (oxymethylene) (POM), 8,9 poly(ethylene oxide) (PEO) 5 , and isotactic-poly(1-butene) (iPB), 10,11 the crystalline segments exhibit helical jump motions in the R c relax- ation temperature range. This type of the motion includes a reorientation around the helical chain axis and a translation along its helical axis. In the systems mentioned previously, it was shown that these motions set-in (as detected by NMR) at temperatures well above the glass transition temperature (T g ) and below melting temperature (T m ) 6,9 and that the correlation times or jump rates obey an Arrhenius behavior. It was also shown that the translation motion in the crystalline region leads to chain diffusion between amorphous and crystalline regions, 12-14 meaning that chain dynamics in the crystallites correlates with the dynamics in the amorphous regions. In the present paper, we raise the question as to whether the crystalline dynamics is affected by the constraints of the polymer chain in the amorphous and/or interfacial regions below T g and if chain dynamics in crystalline segments start near or below T g . Kusanagi et al. compiled densities for the amorphous and crystalline regions for polyolefines as a function of the side-chain carbon number. 15 The crystalline density decreases with increasing number of side-chain carbons, while those in the amorphous region are almost inde- pendent of the side-chain length. However, isotactic- poly(4-methyl-1-pentene) (iP4M1P) with a side-chain carbon number 4 shows a unique density character, namely, that the crystalline density is much lower than expected one from an extrapolation of the other materi- als. It is also lower than that of the amorphous region. We found it therefore interesting to investigate both the molecular structure of iP4M1P and the chain dynamics both in the amorphous and in the crystalline regions. * To whom correspondence should be addressed. (T.M.) E- mail: t-miyoshi@aist.go.jp. Tel: +81-298-61-9392. Fax: +81-3- 359-8166. (D.R.) E-mail: reichert@physik.uni-halle.de. Tel: +49- 345-55-25593. Fax: +49-345-55-27161. † Research Center of Macromolecular Technology. ‡ Martin-Luther-Universita ¨ t Halle-Wttenberg. 6460 Macromolecules 2004, 37, 6460-6471 10.1021/ma049487c CCC: $27.50 © 2004 American Chemical Society Published on Web 07/29/2004